A position switch is one that is responsive to the position of a movable member relative to a fixed or reference member. The switch closes when the movable member is located at a selected position or positions relative to the fixed member. For example, a position switch may be incorporated into the steering column of an automobile or other vehicle to sense the position of a column-mounted shift lever and to activate an external device such as a back-up light when and only when the shift lever is moved to a particular position in the steering column, e.g. the REVERSE position. Accordingly, we will describe the invention in this context. It should be understood, however, that the invention has equal utility in many other applications.
In many vehicles, the steering column comprises a central shaft which connects the steering wheel to the mechanism that turns the vehicle's front wheels. Mounted coaxially with that shaft is a rotative tube which links the column-mounted gear shift lever to the vehicle's transmission. The shift lever is movable to any one of several positions to select a particular gear arrangement in the transmission. For example, the typical shift lever for an automatic transmission includes the positions of PARK, REVERSE, NEUTRAL, DRIVE, SECOND and LOW.
Surrounding the shift lever tube is a stationary outer sleeve which extends from the steering wheel through the dash into the automobile's engine compartment. This outer sleeve serves as a protective housing and a support for various other parts of the steering column, including for example, indicia referencing the aforementioned positions of the gear shift lever.
In the usual arrangement, the gear shift tube is slotted lengthwise and an arcuate opening is provided in the outer sleeve of the steering column to expose the slotted side of the tube. That opening is provided with a sufficient arcuate extent that the slot in the gear shift tube remains exposed through the sleeve opening during rotation of the gear shift tube from one extreme position to the other, i.e. through movement of the gear shift lever from its PARK position to its LOW position.
The position switch is typically mounted to the steering column adjacent the sleeve opening with the switch actuator projecting through that opening into the slot in the gear shift tube. The switch actuator thus moves within the switch housing in response to rotation of the gear shift tube when the gear shift lever is moved from one position to another. When the switch is properly positioned on the steering column sleeve with respect to the slot in the gear shift tube, the actuator will move the movable switch contact into electrical engagement with the stationary contact or contacts in the switch housing only when the gear shift lever is in its REVERSE position so that electrical current is supplied by way of the position switch to the automobile back-up lights to turn on those lights.
In order to have the position switch operate properly to turn on the back-up lights only when the gear shift lever is in the REVERSE position, the position switch actuator and therefore the gear shift tube must be located angularly precisely with respect to the stationary outer sleeve carrying the switch housing and stationary switch contacts. As a practical matter, it is difficult to assemble the steering column gear shift tube and sleeve with a high degree of angular accuracy reliably on a production line. Actually, an angular error between those two members as high as 8.degree. is quite common. Consequently, during production, if all the position switches are fastened to the same location on the steering columns, in a given instance, there may be as much as an 8.degree. angular error in one direction or the other between the stationary switch contacts and the slot in the gear shift tube. Resultantly, the switch may be closed and the back-up lights turned on when the shift lever is in NEUTRAL, PARK or some intermediate setting, with obvious adverse consequences.
In an attempt to avoid this problem, some manufacturers have adopted assembly procedures whereby prior to installing the switch, the assembler moves the gear shift lever to a given position, e.g., its NEUTRAL position. Furthermore, the switch is made with a breakable connection between the actuator and the switch housing which retains the switch actuator in a reference position along its path which corresponds to the position of the gear shift lever that is selected during mounting of the switch, i.e., the NEUTRAL position. The assembler locates the switch housing opposite the arcuate opening in the outer sleeve of the steering column so that the switch actuator projects through the slot in the gear shift tube. Then he secures the housing to the steering column by screws or other comparable means. Next, the assembler moves the gear shift lever away from the NEUTRAL position causing the gear shift tube to move the switch actuator away from its reference position thereby breaking the mechanical connection between the actuator and the switch housing. Theoretically then, since both the gear shift tube and switch actuator were in correspondence initially, when the shift lever is moved into REVERSE, the movable switch contact will be moved into electrical engagement with the stationary switch contacts and the backup lights will be turned on.
In many cases, however, that ideal result does not materialize. This is because during installation of the position switch on the steering column, the switch is often handled roughly with the result that the connection holding the actuator in its reference position is broken prematurely and the actuator shifts from the reference position to some extent. Consequently, when the switch is secured to the steering column with its actuator projecting into the gear shift tube, while that tube may be in its NEUTRAL position, the switch housing (and stationary switch contacts) are no longer referenced to that position. Resultantly, when the shift lever is moved into REVERSE, the actuator is not moved to close the switch. Rather the switch closes at some other position of the shift lever.
Also, in some instances, the assembler in his haste may not properly position the gear shift lever in NEUTRAL prior to mounting the switch, but may locate it at some intermediate position adjacent the NEUTRAL position. Thus when the switch is secured to the steering column even with the switch actuator properly retained in its reference position, the switch housing and stationary contacts are again not referenced to the slot in the gear shift tube. Consequently, when the assembler moves the shift lever in order to break the mechanical connection retaining the switch actuator and shifts into REVERSE, the stationary contacts will not be aligned properly with the REVERSE position of the gear shift tube. Again, then, the switch will close and the brake lights will be turned on at some position of the shift lever other than the REVERSE position. Until now the only ways to alleviate the aforesaid problems known to applicant have been to remove and replace the switch with another properly mounted one or to loosen the original switch's mounting screws and reposition the switch relative to the neutral shift lever position, which positioning requires a special alignment tool. That procedure is obviously quite time consuming and costly, particularly if the problem is not discovered until final inspection of the vehicle.
Also some prior position switches of this general type have tended to be relatively complicated structures requiring a relatively large number of parts which have to be assembled using special tools thereby making the overall switch relatively expensive and installation procedure relatively involved.